NMEA message checksum

nmea_chksum.py

import sys, getopt


def main(argv):
    if len(argv) < 1:
        print "Put a message - like GPVTG,,T,,M,0.191,N,0.354,K,D"
        return

    msg = argv[0]
    checksum = 0
    for item in msg:
        byteitem = ord(item)
        checksum ^= byteitem

    print "$%s*%s" % (msg, str(hex(checksum)[2:]))

if __name__ == "__main__":
   main(sys.argv[1:])